The present invention relates to a hydraulic circuit including multiple fixed displacement pumps and corresponding compensator unloading valves which are phased so that one pump supplies the fluid demand of the circuit until the demand exceeds that pump's capacity and then another pump adds flow to supply larger fluid demands.
It is common in earth-working equipment, such as backhoes, front-end loaders and the like, to have a bucket or shovel mounted on a tractor to be raised and lowered, tilted, or otherwise moved into the correct attitude by an appropriate mechanism for the work being performed at the moment. Such adjustments of the bucket or shovel are commonly made by hydraulic cylinders supplied with fluid pressure from a suitable pump.
A common mode of operation in earth-working is to move a bucket or shovel into a pile of material. The hydraulic systems for such earth-working applications require a high volume of fluid at low pressure to rapidly move the cylinder piston rods and, therefore, the bucket or shovel to the work. Then, low fluid volume under high pressure must be available to provide the necessary tilting of the bucket or shovel to break a portion of the material loose from the work pile or lift the material in the bucket or shovel.
One of the prior art approaches has been to provide two fixed displacement pumps to supply the required fluid under pressure for the hydraulic circuit. This allows for high flow at low pressure and low flow at high pressure for rapidly moving the bucket to the work and then working the bucket against a load without requiring increased power from the engine. While the use of multiple fixed displacement pumps permits a more energy efficient system, there has been a need for an improved multiple pump hydraulic circuit which is more fuel efficient and generates less heat. Thus, the present invention provides a more energy and cost efficient system than known circuits utilizing multiple fixed displacement pumps.